Light-sensitive material and process of its preparation



ing it in a dilute aqueous ammonia solution.

United States Patefit- 2,703,283 LIGHT-SENSITIVE rnocnssor rrs PREPARATION John Eggert, Zurich, Switzerland No Drawing. Application ;March 6, 1951, Serial No. 214,217

-2 Claims. (CI. 95-47,)

This invention relates to photography and more particularly to the use of light-sensitive detonable endothermic compounds for the direct formation of photographic images.

Conventional photographic and phototechnical materials respond to the action of light with primary reactions which correspond to a quantum yield smaller than one. Frequently, the photochemical changes induced in the materials by the action of light are only of a latent nature. Consequently, these changes must be increased and intensified by a development process which yields the actual image. The developed picture must be subjected to an additional fixing operation which protects it against further exposures.

Previous attempts to employ endothermic lightsensitive substances for photographic and phototechnical purposes were unsuccessful. These experiments were started with the expectation that the action of light would trigger a chain reaction with a quantum yield greater than one. However, all of these experiments were abandoned for a variety of reasons. For example, E. Roderer (Zeitschr. f. anorgan. Chem. 226, 145; 1936) stresses in the only available publication on this subject, that the risk of explosions could not be avoided. Furthermore, the handling of nitrogen iodide which had been chosen as the light-sensitive substance involved several undesirable complications. The anticipated chain reaction Was not observed when other endothermic compounds such as silver azide and silver carbide were tested.

It is an object of the present invention to provide light-sensitive materials which are stable in ordinary light and which, upon exposure with flashlight of short duration and adequate intensity, undergo a chain reaction and give a quantum yield greater than one.

It is another object of the invention to provide a process for the production of novel, light-sensitive materials.

It is a further object of the invention to provide processes of forming direct positive images without the use of those secondary chemical processes which are known as photographic development.

Other objects of the invention will be apparent from the following description taken in connection with the claims.

Contrary to accepted beliefs, I have found that explosives of high impact sensitivity can be detonated by the action of flashlight of sufl'icient light intensity.

I have further found that the shortcomings of the prior art can be avoided if an endothermic substance of great inherent lability and sensitivity is stabilized or selectively inactivated by embedding it in a very finely divided form into a carrier, support or binding material such as absorbing cellulose layers, hardened filter paper, asbestos paper or other fibrous materials. Among the detonable, endothermic substances suitable for the purpose of the present invention are the following impact or primer detonators: nitrogen iodide, silver fulminate, silver azide, silver carbide (silver acetylide) and silver oxalate. These compounds are formed directly on the fibers by impregnating the carrier with av solution of one of the components and subsequently treating the still moist carrier with the second component. For example, a flashlight sensitive nitrogen iodide paper is prepared by treating a hardened filter paper with a solution of iodine in potassium iodide and subsequently exposing it to ammonia vapors, or soak- Similarly, a silver carbide paper is prepared by bathing a hardened filter paper in a silver nitrate solution, removing any 2,703,283 *P atentetl Mar. 1955 adhering diquid mechanically, for example, 'byacentrituging and cont-acting the moist paper with acetylene vapors.f,

Other endothermic silver salts can be precipitated on the fibers by immersing the fibrous carrier .in an aqueous solution of silver nitrate, removing any excess of liquid and bathing the carrier in :a solution of 'a water-soluble salt :of fulminic, azoic 'or oxalic acid, e. .g., air-alkali fulminate, azide or oxalate. After washing out or draining otf of any excess-of the above solution, the impregnated material is dried at moderate temperatures over .a suitable desiccant such as potassium hydroxide, magnesium perchlorate, calcium chloride, calcium oxide, phosphorus :pentoxi'de and the like. The presence of ammonia vapors is 'desirable when nitrogen iodide .paper .is to be dried. The dried materials which contain the highly explosive, detonable endothermic compounds absorbed in a finely divided form are remarkably stable and safe to handle. They can be cut, contactprinted and chemically toned without danger of premature detonation. This stability is very surprising since endothermic compounds such as nitrogen iodide or silver fulminate, when not absorbed by the fibrous materials, are highly sensitive and explode on percussion. Some of them are known to explode at the slightest touch, even that of a feather.

The flashlight sensitive materials of this invention can be handled safely in subdued daylight or artificial light and do not decompose when stored under ordinary conditions. They detonate only when exposed to photographic speed lights, flash lamps or flashlights of adequate light intensity in the visible range. The exposure to flashlight triggers a chain reaction by which one quantum of light triggers the detonation of numerous endothermic molecules. Images obtained by contact printing with flashlight are immediately visible but can be converted by suitable toning or fixing steps into pictures of permanent stability even to subsequent flashlight exposures.

The following example describes in detail the operation of this invention but it is to be understood that it is inserted merely for purposes of illustration and is not to be construed as limiting the scope of the invention.

Example A sheet of hardened filter paper was soaked at room temperature in an aqueous iodine-potassium iodide solution containing about 20% of potassium iodide and 10% of iodine. After mechanical removal of excess liquid, the paper was placed for about 15 minutes in an aqueous solution of ammonia having a specific gravity of 0.88, until it had acquired a deep brown-black coloration. After drying at room temperature in the presence of ammonia vapors over a mixture of calcium oxide and ammonium chloride, the paper was ready for printing. It was exposed with a flashlight of adequate light intensity through a positive transparency and yielded immediately a direct positive having a very pleasing appearance. The printing time and the amount of light required was but a fraction of that needed for the exposure or a print-out or diazo-type layer.

The nitrogen iodide image can be readily converted into a silver image by the following method. The print was bathed in alcohol for about 5 minutes, then immersed for about 10 minutes in a 5% solution of silver nitrate, washed, and afterwards transferred to a 10% aqueous solution of sodium sulfite in which it was kept until the brownish-black coloration had disappeared and the nitrogen iodide had been converted into silver iodide. The paper was rinsed briefly. The silver iodide was now reduced to metallic silver by immersing the paper in an alkaline aqueous sodium stannite of about 5% strength until a black-and-white silver image appeared. After washing and drying, a brilliant print having full tonal range, excellent sharpness and showing all highlight and shadow details was obtained. The keeping qualities of the print were infinite.

I claim:

1. The method of preparing a direct positive print which comprises incorporating nitrogen iodide as a detonable endothermic substance in a finely divided form into a highly absorbent cellulosic carrier material by impregnating said absorbent carrier material with an aqueous iodine-potassium iodide solution, treating the tion, thereby forming finely divided nitrogen iodide in the carrier, exposing the material thus obtained after drying through a transparency with visible light of short duration and high intensity produced by a photographic speedlight, thereby detonating part of the nitrogen iodide, the extent of detonation being directly proportional to the amount of light transmitted by the various areas of said transparency.

2. The process of preparing a direct positive copy without reversal development which comprises impregnating an absorbent paper with an aqueous iodinepotassium iodide solution, treating the moist paper subsequently with an aqueous ammonia solution thereby forming finely divided nitrogen iodide in the paper, exposing said paper after drying with a photographic speed light through a transparency thereby detonating part of the nitrogen iodide commensurate to the amount of light passing through the transparency, converting the remaining nitrogen iodide into silver iodide and reducing the latter to metallic silver with an alkaline aqueous sodium stannite solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,939,232 Sheppard et a1. Dec. 12, 1933 1,976,302 Sheppard et a1. Oct. 9, 1934 2,095,839 Sheppard et a1 Oct. 12, 1937 2,129,242 Sheppard et al. Sept. 6, 1938 2,414,839 Schoen Jan. 28, 1947 OTHER REFERENCES Eastman Kodak Research Laboratories Monthly Abstract Bulletin (February 1943, page 41).

Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry (1928), vol. 8, pages 607 and 608. Pububy Longmans, Green & Co., New York, N. Y. 

1. THE METHOD OF PREPARING A DIRECT POSITIVE PRINT WHICH COMPRISES INCORPORATION NITROGEN IODIDE AS A DETONABLE ENDOTHERMIC SUBSTANCE IN A FINELY DIVIDED FROM INTO A HIGHLY ABSORBENT CARRIER MATERIAL WITH AN IMPREGNATING SAID ABSORBENT CARRIER MATERIAL WITH AN AQUEOUS IODINE-POTASSIUM IODIDE SOLUTION, TREATING THE MOIST PAPER SUBSEQUENTLY WITH AN AQUEOUS AMMONIA SOLUTION, THEREBY FORMING FINELY DIVIDED NITROGEN IODIDE IN THE CARRIER, EXPOSING THE MATERIAL THUS OBTAINED AFTER DRYING THROUGH A TRANSPARENCY WITH VISIBLE LIGHT OF SHORT DURATION AND HIGH INTENSITY PRODUCTED BY A PHOTOGRAPHIC SPEEDLIGHT, THERBY DETONATING PART OF THE NITROGEN IODIDE, THE EXTENT OF DETONATION BEING DIRECTLY PROPORTIONAL TO THE AMOUNT OF LIGHT TRANSMITTED BY THE VARIOUS AREAS OF SAID TRANSPARENCY. 